Conventionally, as a technique of enabling power transmission in a contactless manner, there has been known an electromagnetic induction system in which current is passed through one of two adjacent coils, energy is converted into a magnetic field, and then electromotive force is generated in the other coil. Further, as another method, there has been known a radio wave system in which current is converted into an electromagnetic wave, and energy is transmitted via an antenna. The former is suitable for a case where large power is handled, but, a power transmission distance thereof is generally short. The latter has a long power transmission distance, but, control of a transmission direction is difficult and thus a transmission efficiency is low.
On the contrary, there has been known a magnetic field resonance system in which a power transmission resonator is disposed in a power transmission device, a power reception resonator is disposed in a power reception device, and the resonators are coupled to each other by magnetic field resonance. According to the magnetic field resonance system, there are characteristics such that it is possible to obtain a high transmission efficiency even if there is a certain amount of separation distance, and there is little influence due to axis deviation and the like.
When power transmission is performed by using a plurality of power transmission resonators in this magnetic field resonance system, there is a possibility that the plurality of power transmission resonators are mutually magnetic-field-coupled, resulting in that power is transmitted from a certain power transmission resonator to another power transmission resonator. This lowers a transmission efficiency, which is a problem.